Christie Brinkley, 63, is joined by her daughters, Alexa Ray Joel, 31, and Sailor Brinkley Cook, 18, in the magazine, on newsstands Feb. 15, and she says their encouragement was key to getting her back in her bikinis.

“My first thought was, ‘At my age? No way!'” she tells PEOPLE exclusively in this week’s issue. “When I turned 30, I was like, ‘This is the last time I’m posing in a bathing suit!’ When this issue comes out, I’ll be 63. I thought, ‘Those days are over.’ But to get to do it with my girls, I thought, ‘One last go!'”